Gas monitors are frequently used in conjunction with respirators in intensive care units, particularly in the case of premature infants suffering from respiratory distress syndrome. A medical staff's ability to evaluate a neonate's oxidative status, and to detect any status change during respiratory therapy, would be significantly assisted by a monitor which measures and displays the patient's whole-body oxygen consumption rate and carbon dioxide production rate. Knowledge of the whole-body oxygen consumption rate enables the staff to determine whether the gas mixture supplied through the respirator contains the proper quantity of oxygen. Consumed oxygen and expired CO.sub.2 measurements are also used to calculate metabolic rate, Respiratory Exchange Ratio (RER) and cardiovascular function.